Cryogenic separation of fluids associated with a power cycle



Oct. 6,1970 K, LA FLEUR 3,531,942

CRYOGENIC SEPARATION OF FLUIDS ASSOCIATED WITH A POWER CYCLE Filed Feb.12, 1968 2 Sheets-Sheet 1 I 1 1 ll? GAS IN 42 l 4 4| "2' y B 4 lAFTEQCOOLEE COMPQ. 37

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CRYOGENIC SEPARATION OF FLUIDS ASSOCIATED WITH A POWER CYCLE Oct. 6,1970 Filed Feb. 12, 1968 2 Sheets-Sheet 2 AT EXPANDEE AT HEATER ATEEGEN. 3

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ENTQOPV INVENTOR. JQMES K. 110F050? United States Patent 3,531,942CRYOGENIC SEPARATION OF FLUIDS ASSOCI- ATED WITH A POWER CYCLE James K.La Fleur, 6342 Mulholland Hwy., Los Angeles, Calif. 90028 Filed Feb. 12,1968, Ser. No. 704,824 Int. Cl. F25j 3/06; F01k 3/18 US. Cl. 6223 1Claim ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The Lindedual-pressure liquefaction cycle is wellknown. It consists ofcompressing and cooling a gas to the point where a subsequentJoule-Thomson expansion causes partial liquefaction. This firstexpansion is to an intermediate pressure somewhere between the highpressure of the system and the compressor-input low pressure, which isusually atmospheric. From a phase separator the portion which is stillgas is returned to an intermediate pressure point on the compressor andrecycled. The liquid phase is then further Joule-Thomson expanded to astill lower temperature, down to the low pressure of the system(atmospheric). It is again phase separated. The liquid phase is removedas useful product, i.e., liquefied gas, such as air. The gas portion orphase is returned to the low-pressure input of the compressor.

Employment of the intermediate pressure gas by reinjecting it into thecompression cycle is relatively inefficient, and it is the purpose ofthis invention to markedly increase the basic efficiently of this cycle.

SUMMARY OF THE INVENTION In accordance with the present invention, thebasic Linde dual-pressure system is modified by taking the intermediatepressure gas, after separation and after heat exchange has raised itstemperature substantially to ambient, and significantly increasing itstemperature by adding heat from an external heat source not associatedwith the heat exchange step-s implicit in the system itself. Theintermediate pressure gas may, of course, also be subjected to heatexchange, as in the basic Linde system. After this external heating, thegas is ready for very efficient use in a heat expansion engine, in whichits pressure is lowered to the low pressure of the system, e.g.,atmospheric. It may be then heat exchanged with the gas incoming to theexpansion motor, and returned to the low pressure input of thecompressor.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1, consisting of FIGS. 1A and 1B,illustrates a first form of the present invention, involving liquefac"ice FIG. 1B is a temperature-entropy diagram illustrating the statesand conditions through which the substance passes in its transit throughthe cycle of the present invention.

FIGS. 2A and 2B are corresponding figures for the non-liquefaction formof the present refrigeration cycle.

Referring to FIG. 1A, 11 designates a compressor means powered in anysuitable manner, represented, for example, by the drive shaft 12. Inputgas is fed to the compressor means 11 at 13. The gas may be a single gasor a mixture of gases, such as air. The gas is compressed from arelatively low pressure at 13, typically, but not necessarily,atmospheric, to a relatively high pressure at the output 14 and thencooled in an aftercooler 16. The aftercooler is typically an ambientheat exchanger in which the rise in temperature effected by thecompression in 11 is dissipated to the air or through some other ambientmedium, such as a water cooling system. After being cooled as close toambient temperature as is economically feasible, the compressed gas isapplied at 17 to a heat exchanger 18, where it is further cooled anddelivered at 19 to a throttle valve 21. The gas is Joule- Thomsonexpanded across the valve 21, and in so doing, its temperature islowered to the liquefaction temperature. Substance, now part gas andpart liquid, is delivered at 22 to a separator 23.

The liquid phase settles to the bottom and flows out a lower outlet 24.The gaseous phase rises to the top of the separator 23 and flows out anupper outlet 26. The pressure in the separator 23, i.e., at the throttleoutput 22, is at an intermediate point, substantially below the highpressure at 14, but still substantially above the low pressure at 13.

The liquid emerging at 24 is further throttled, through a throttle valve27, from the intermediate pressure down substantially to the lowpressure at 28. It is then applied to a second liquid/ gas separator 29.The Joule-Thomson expansion across 27 lowers the temperature stillfurther. From the second separator 29 liquefied substance is taken outat 31, this being the end poduct of the system. The gaseous fraction ofthe substance existing in separator 29 is taken out at the top outlet 32and applied through the heat exchanger 18 to return to the input 13 ofthe compressor 11. In passing through the heat exchanger 18, thislow-pressure, very cold gas receives heat from the high-pressure gasflowing from 17 to 19, and thus serves to pre-cool the high pressure gasbefore it is applied to the throttle valve 21. The coldintermediatepressure gas at 26 is also applied to the heat exchanger 18and it also receives heat from the high-pressure gas, thus also coolingit.

The apparatus and thermodynamic cycle described up to this point isessentialy the prior art Linde dual-pressure liquefaction system. In theLinde system, the intermediate-pressure gas from point 33 isrecompressed in the compressor 11, "being introduced at an intermediatepressnre point in the compressor.

In accordance with the present invention, however, the intermediatepressure gas from 33 is applied to an expansion engine 34 after beingheated substantially, by passage through an external heater 36, whichrepresents a source of heat independent of the heat exchanges which takeplace between various states of the substance as it flows through thesystem. If desired, the gas, prior to subjection to the heat source 36,may be heated in a heat exchanger 37.

From the output 38 of the heater 36, the gas is expanded in theexpansion engine 34, which derives or extracts work therefrom, at thesame time lowering the pressure andtemperature. From the output 39 ofthe engine 34, the gas, still considerably warmer than the gas at 33,gives up heat in the heat exchanger 37. It may be further cooled in anaftercooler 41 by giving up heat to an ambient medium, such as air.

In the expansion engine 34 the gas is expanded substantially to the lowpressure at 13; so from the aftercooler 41 it is ready to rejoin thelow-pressure gas taken from the separator 29, and thence be applied at13 through the input to the compressor 11. Since substance was extractedfrom the system 31 in the form of liquid, it must be made up a 42 by aconstant supply of makeup gas which joins the re-cycled gas at the inputIt is usually found desirable to maintain the pressure at 13substantially at atmospheric, although it may be either above or belowatmospheric. If below atmospheric, however, there is involved operationswith various types of vacuum equipment which is costly and cumbersome.If above atmospheric, the maximum use is not made of the gas, either inexpansion across the valve 27 or in the engine 34. However, in certaincircumstances, the makeup gas 42 comes in at a pressure aboveatmospheric, and under these circumstances this determines the inputpressure at 13. Alternatively if the makeup gas is received at apressure significantly above atmospheric, the system may be designed sothat this pressure prevails at 33. In this case, the makeup gas isinjected at 33, and 13 is maintained at substantially atmospheric. Theoptimum high pressure at 17/ 19 will depend upon the gas being used, butin general it is the pressure at which the isenthalpic slope is zero.The intermediate pressure at 26/33 is preferably somewhere between thelow pressure at 13 (atmospheric) and the critical pressure of the gas.

The temperature of the gas at 19' must be below the Joule-Thomsoninversion temperature of the gas. For some substances and under certainconditions, this may require auxiliary cooling, which may be injected inthe form of auxiliary refrigeration at 43. For certain applications,this also increases the cycle efficiency. Alternatively or additionally,a portion of the gas flowing through the heat exchanger 18 may be splitout at 44 and applied to an expansion engine 46, the output of which isat the low pressure of 13 and rejoins the expanded gas at 47. This isessentially the known Claude cycle and is used to provide furthercooling in the heat exchanger 18 in order to lower the gas at 19 to asufficiently low temperature. Alternatively, the input 44 to engine 46may be taken from line 26/33, rather than line 17/19.

Mechanical power output from the expansion engine 34, represented by theshaft 48, may be directly connected to the compressor input shaft 12, ormay generate power for use elsewhere. The same may be said for poweroutput from expansion engine 46.

The system may be designed so that the work output equals the work inputrequired by the compressor 11, in which case all of the energy injectedinto the system is done so at the heater 36, and external power is notrequired except to initially drive the compressor 11 up to steady-stateoperation. Alternatively, the power output may even be designed toexceed the power requirements of 11, in which case the power may be usedelsewhere, or the system may be designed so that the power output fromthe engine 34 '(and 46 if employed) is less than that required by thecompressor 11, in which case external power at 12 is constantlyrequired. The design of the system in this regard is dependent simplyupon the economy and availabiliy of power required at 11 vis a vis fuelrequired at 36.

The thermodynamic cycle to which the substance is subjected isillustrated in the temperature/entropy diagram of FIG. 1B. In thisfigure the reference points on the diagram correspond to the similarlynumerated points in the apparatus of FIG. 1A.

The substance in gaseous form is injected into the compressor 11 atpoint 13 and at temperature T1 which is customarily, although notnecessarily, the ambient temperature. As noted hereinbefore, thepressure represented by the line P1 is the low pressure of the systemand is preferably, although not necessarily, atmospheric. The gas iscompressed to the high pressure represented by the line P2. Theaggregate effect of the compressor 11 and aftercooler 16 is to make thecompression essentially iso thermal, as shown by the line 11 in FIG. 1B.

From the point 17, the gas is cooled at substantially constant pressureP2 in the heat exchanger 18 to the point 19. A Joule-Thomson expansionis effected at 21 to bring the substance to the point 22 within thetwo-phase locus 51. The liquid phase is subjected to further Joule-Thomson expansion at 27, from the point 24 to 28. The liquid phase, nowstill further cooled, is removed at 31. The separator 29, operating atpressure P1, now delivers the gas phase at 32 to the heat exchanger 18where it takes on heat from the gas at pressure P2 and rises to thetemperature T1, as shown at point 13. The substance in separator 23existing at the intermediate pressure P3 is separated in gaseous phaseat the point 2.6, also taking on heat in 18, to rise to the temperatureT1.

The cycle of FIG. 1B described up to this point, as noted, issubstantially the Linde dual-pressure system.

In accordance with the present invention, the intermediate pressure gaSat P3, instead of being merely raised to ambient temperature T1, issubjected to the heat of the heat exchanger 37 and to further heating inthe external heater 36; so it is raised to temperature T2 at point 38.It is then expanded in the engine 34, which extracts useful work, dropsthe temperature to a point intermediate T1 and T2, and lowers thepressure to the lowpressure point P1, as shown at 39. From 39 to 13, thegas gives up heat in the heat exchanger 37 and aftercooler 41, andreturns to the point 13 to be re-cycled.

As noted hereinbefore, substance extracted at 31 in liquid form is madeup at 42 in gaseous phase.

Because of the significant increase in gas temperature from T1 to T2,the work extracted at 34, unlike a typical Claude cycle, represents aconsiderable portion of the work or power required to operate thesystem.

The essential attributes of the system described in FIGS. 1A and 1B areas follows:

There is an initial J oule-Thomson expansion from some optimum pressureP2 to an intermediate pressure P3, between the low pressure P1(atmospheric) and the critical pressure of the gas; followed by divisionof the substance. One portion (in FIG. 1B, liquid) is further Joule-Thomson expanded to the low pressure P1, while the other portion iswarmed by heat exchange with the high-pressure gas at P2 and then isfurther externally heated to the high-temperature T2, at which itsemployment in an expansion engine 34 becomes very efficient. Expansionin the engine reduces the gas substantially to the low-pressure P1, andit rejoins the first portion to be re-cycled into the compressor.

The system described is applicable not only to the liquefaction ofcryogenic gases, but may be employed generally in any three-pressurerefrigeration system, even though no liquefaction takes place. This isillustrated in FIG. 2A, which is the counterpart of FIG. 1A, except thatthe gas is not necessarily liquefied. FIG. 2A il1ustrates only thoseportions of the system which differ from FIG. 1A, the correlationbetween the two figures readily being evident.

In FIG. 2A, the high-pressure gas is throttled, as in FIG. 1A, throughthe restriction or valve 21. From 21, the gas enters any suitabledivider, shown schematically at 23, where a portion of the gas, now atintermediate pressure P3, is taken off at 26 and applied to the heatexchanger 18, the same as in FIG. 1. The other portion of the substance,also in gaseous phase, is removed at 24 and further throttled at 27,down to the low-pressure P1 existing at 28. These two steps, while notliquefying the gas, each successively reduce its temperature. It is thenused to refrigerate any medium which is to be cooled, by being appliedto the heat exchanger 29'. The

medium to be cooled flows in at 61 and out at 62. The gas then returnsat 32, as in the case of FIG. 1, through the heat exchanger 18 andthence back to the low-pressure input 13 of the compressor 11.

The dynamic cycle to which the gas is subjected is shown in FIG. 2B. Thecorrespondence between FIG. 2B and FIG. 13 will be readily evident. Thegas is cooled to the point 19, then throttled in 21 before being dividedat 23' into a portion of intermediate pressure P3, and another portion,which is throttled from pressure P3 down to pressure P1 in the expansionvalve or throttle 27. Thereafter the two portions of the substance at P3and P1, respectively, are heated and treated the same as in the case ofFIG. 1B.

Whereas the present invention has been shown and described herein inwhat is conceived to be the best mode contemplated, it is recognizedthat departures may be made therefrom within the scope of the inventionwhich is, therefore, not to be limited to the details disclosed herein,but is to be afforded the full scope of the invention as hereinafterclaimed.

What is claimed is:

1. Process for the liquefaction of a substance from gaseous to liquidphase, comprising:

compressing the substance in gaseous phase from substantiallyatmospheric pressure to a relatively high pressure,

cooling said substance to below its inversion temperature,

Joule-Thomson expanding said substance to an intermediate pressure toliquefy a first portion thereof, a, second portion remaining in gaseousphase,

Joule-Thomson expanding said first portion to substantially atmospherictemperature, a fraction of References Cited UNITED STATES PATENTS1,571,461 2/1926 Van Nuys 6239 2,520,626 8/1950 De Baufre 6288 2,952,9849/1960 Marshall 6239 2,956,410 10/1960 Palazzo 6223 3,119,677 1/1964Moon et a1. 6223 1,379,102 5/1921 Iefferies.

NORMAN YUDKOFF, Primary Examiner A. F. PURCELL, Assistant Examiner US.Cl. X.R.

